Not enough gear for the speed and
the rider can't keep up; too much gear and the rider can't accelerate fast
enough. Small gear changes make a difference. This section gives
a quantitative basis for picking one gear over another.
Gear Chart
A gear chart gives a relation between the forward motion of
a bike and one revolution of the pedals. It is derived from the time
of ordinary bikes (the old ones with the very large front wheels that were
driven directly by the pedals without the benefit of gears). The values
in the table are equivalent to the diameter of the ordinary's front wheel.
The values in the table are (Chainring Teeth\Cog Teeth) x Wheel
Diameter and the units are inches.
Gear Inches
|
46 |
47 |
48 |
49 |
50 |
51 |
52 |
53 |
13 |
93.6 |
95.7 |
97.7 |
99.7 |
101.8 |
103.8 |
105.8 |
107.9 |
14 |
86.9 |
88.8 |
90.7 |
92.6 |
94.5 |
96.4 |
98.3 |
100.2 |
15 |
81.1 |
82.9 |
84.7 |
86.4 |
88.2 |
90.0 |
91.7 |
93.5 |
16 |
76.1 |
77.7 |
79.4 |
81.0 |
82.7 |
84.3 |
86.0 |
87.6 |
The following table shows the distance in meters the bike
will travel in one revolution of the pedals for a given chainring, cog,
and wheel diameter combination:
Gear Rollout
|
46 |
47 |
48 |
49 |
50 |
51 |
52 |
53 |
| 13 |
7.470 |
7.633 |
7.795 |
7.957 |
8.120 |
8.282 |
8.445 |
8.607 |
| 14 |
6.937 |
7.087 |
7.238 |
7.389 |
7.540 |
7.691 |
7.841 |
7.992 |
| 15 |
6.474 |
6.615 |
6.756 |
6.896 |
7.037 |
7.178 |
7.319 |
7.459 |
| 16 |
6.070 |
6.202 |
6.333 |
6.465 |
6.597 |
6.729 |
6.861 |
6.993 |
| 
